Contemporary backplanes, also referred to as motherboards, serve as a communication medium for the exchange of electronic signals between a plurality of daughter cards. Each daughter card generates communication signals, for example, data bus signals, address bus signals, and control signals. The signals are distributed to connectors mounted along an edge of the daughter card. The daughter card connectors mate with a corresponding set of connectors on the backplane for providing electrical interconnects between each daughter card. The backplane distributes the signals between daughter cards along various communication paths as well as to input/output I/O connections via cable assemblies.
A chassis, commonly referred to as a xe2x80x9ccard cagexe2x80x9d, houses the backplane, daughter cards, and corresponding connectors. Backplane connectors are spaced on equidistant rows along the backplane, each row defining a card slot. Card guides are mounted, in pairs, one pair for each slot, along the top and bottom of the chassis for guiding an inserted daughter card to ensure proper mating of the connectors.
Contemporary card cages are commonly comprised of extruded rails supported at each end by side panels, or xe2x80x9cside-platesxe2x80x9d. In addition to providing rigidity in the card cage, the rails serve to support the card guides. Each side panel includes precision-drilled holes that provide accurately-positioned locations for the mounting of the extrusion rails. A xe2x80x9cUxe2x80x9d dimension identifies the vertical position of the hole location (where U represents 1.75 inches). Card cages are commonly sized according to multiples of U units, for example, 3U, 6U, 9U, etc. The horizontal positions of the hole locations are commonly identified in multiples of millimeters, according to standard industry practice.
The extruded rails are configured to accept additional parts such as nut bars, adapted for securing front and rear panels, and backplanes, to the subrack. Attachment for the card guides is provided either by a spacer strip with punched holes, or by directly punching areas of the extrusion.
As electronics become more sophisticated, there is an ever-increasing demand on the backplane. It has recently become common for boards and connectors to not only be inserted at the front side of the backplane, at the connectors, but also at the rear side of the backplane, for example at the connector shrouds, to allow for increased communication, improved servicing, and more robust testing capability. Existing chassis configurations do not allow for convenient rear access because the rear chamber portion of the chassis, that is, the region of the card cage behind the backplane, must extend as far as the length of the largest rear-mounted daughter card, in order to protect the cards. When rear access is required by an operator or machine, the operator must reach deeply into the rear chamber in an awkward manner that is risky to both operator and nearby electronics. Additionally, a chassis employing side panels and lateral extrusions is difficult to assemble and install as they commonly require multiple-point fastener locations. Furthermore, such chassis are relatively weak and unstable, and they are subject to excessive rattling and vibration.
Along with physical demands, a card cage must meet the increased demands on electromagentic interference (EMI) shielding requirements. In general, as the frequency of system operation increases, signal wavelengths decrease, and so the minimum allowable gap in shielding likewise decreases. Many contemporary card cage configurations exhibit EMI shielding that is inadequate for modern electronics systems, both at frame joints and at seams.
The present invention is directed to a card cage assembly that overcomes the limitations described above. Specifically, the configuration of the present invention allows for improved access to the rear panel of the backplane, while providing for enhanced EMI shielding. In this manner, the present invention provides a cost effective card cage unit that is relatively simple to assemble and provides improved lateral and torsional rigidity over conventional configurations.
In a first aspect, the present invention is directed to an improved card cage configuration. First and second side panels, in combination with top and bottom covers, form the card cage. The top and bottom covers are adapted for removably mounting to the side panels, and, when mounted, provide lateral rigidity to the card cage. At least one of the top and bottom covers comprises a front portion and a rear portion. The front portion of the cover is preferably separable from the rear portion such that one of the front and rear portions is removable from the side panels, while the other of the front and rear portions remains mounted for providing lateral rigidity.
In a preferred embodiment, the front and rear portions of the cover each comprise lateral members for coupling the cover to the side panel, and a bridging member coupled between the lateral members. The bridging member preferably comprises first and second bridging sub-members spaced apart by a screening member. At least one of the bridging sub-members includes inserter/extractor leveraging apertures. The screening member preferably comprises EMI screening having apertures to permit air flow therethrough, while maintaining suitable EMI shielding.
The lateral members preferably comprise a slot for receiving an edge of the side panel so as to mount the lateral member on the side panel, and a seat parallel to the slot and orthogonally oriented relative to the slot for seating a surface of the bridging member relative to the lateral member. A face parallel to the slot includes mounting features for mounting the lateral member to the side panel. The seat and slot are preferably adapted for receiving an EMI gasket. The EMI gasket preferably comprises continuous tubular gasketing material. The bridging member of at least one of the front and rear portions preferably includes an EMI gasket substantially continuous across a portion of the interface of the front and rear portions to ensure proper EMI shielding across the length of the interface.
In a second aspect, the present invention is directed to a card cage having substantially continuous EMI shielding. First and second side panels and top and bottom covers together form the card cage. The top and bottom covers are adapted for removably mounting to the side panels for providing lateral rigidity to the card cage. The covers include lateral members for coupling the cover to the side panel. Each lateral member is adapted for interfacing with a feature of the side panel along the length of the lateral member so as to provide substantially continuous EMI shielding continuity therebetween. The covers further comprise a bridging member coupled between the lateral members. The bridging member is adapted for interfacing with a feature of the lateral member along the length of their intersection so as to provide substantially continuous EMI shielding continuity therebetween.
In a preferred environment, at least one of the top and bottom covers comprises a front portion and a rear portion. The front and rear portions are preferably separable from each other such that one of the front and rear portions is removable from the side panels while the other of the front and rear portions provides lateral rigidity.
In a third aspect, the present invention is directed to a ember for coupling a cover and side panel of a card cage. The member includes a body extending along a longitudinal axis of the member. A slot is formed in the body parallel to the longitudinal axis, for receiving an cage of a side panel. A seat is likewise formed in the body parallel to the longitudinal axis for receiving a cover positioned orthogonal to the side panel.
In a preferred embodiment, the slot includes a bore at a terminus of the slot adapted to receive a resilient EMI gasket to be embedded in the slot, for example a tubular gasket. The seat preferably includes a groove for receiving an edge of the cover. The groove preferably includes a bore at a terminus of the groove adapted to receive a resilient EMI gasket to be embedded in the groove.
The lateral member preferably further includes a locking feature adapted for removably securing the lateral member to a side panel. The locking feature may comprise a pin adapted to interface with a corresponding channel on the side panel.